A method for preparing a metal-based porous ceramic composite membrane

Abstract

The present invention provides a method for preparing a metal-based porous ceramic composite membrane, comprising the steps of: S1 coating a suspension on the inner surface of a porous ceramic tube to form a ceramic inner coating; S2 rolling a metal plate into a tube, inserting it into a mold and clinging to the inner surface; S3 passing the porous ceramic tube through the hollow part of the mold in S2, and arranging an annular connector at one end of the mold, forming a cavity between the outer wall of the ceramic tube, the inner wall of the mold and the connector; S4 filling the cavity with metal powder and sealing it at the other end of the mold to form an assembly; S5 sintering the assembly at high temperature, the ceramic inner coating forming a ceramic film layer, the metal powder forming a metal film layer, removing the mold, peeling off the metal plate, and obtaining a metal-based porous ceramic composite membrane. The metal plate and the metal powder of the present invention diffuse mutually at high temperature, and the metal plate can play a good fixing role on the metal powder, effectively reducing the axial shrinkage of the metal film layer after high-temperature sintering.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy porous material preparation, and specifically relates to a method for preparing a metal-based porous ceramic composite membrane. Background Art

[0002] The membranes used in membrane separation equipment can be divided into two categories according to their materials: organic membranes and inorganic membranes. Among them, inorganic membranes can be divided into ceramic membranes and metal membranes.

[0003] Organic membranes are more susceptible to corrosion by organic solvents during use, are not resistant to strong acid and alkali corrosion, are not heat-resistant, and have a short lifespan; compared to organic membranes, ceramic membranes, as a commonly used membrane material, have the advantages of good chemical stability, high mechanical strength, high temperature resistance, and high separation efficiency. Although ceramic membranes have higher strength than organic membranes, the brittleness of the general ceramic matrix is ​​relatively large, which makes ceramic membranes prone to sudden damage during use. In addition, they must rely on rubber seals and have poor heat and solvent resistance. Although metal membranes have the advantages of high strength, weldability, heat resistance, and solvent resistance, their filtration accuracy is still at the microfiltration level, and it is difficult to meet the use requirements of high-precision filtration systems. The metal-ceramic composite membrane is a new type of special membrane material that combines the high precision of ceramic membranes with the high strength and weldability of metal membranes.

[0004] Metal-ceramic composite membranes are usually prepared by preparing a ceramic layer on the surface of a porous metal substrate, but the preparation is difficult due to the large difference in thermal expansion coefficients between metal and ceramic; another solution is to add a macroporous metal protective layer to the outer surface of the porous ceramic. Patent CN111229058B discloses a process for preparing a ceramic composite membrane with a metal protective layer, including a ceramic membrane, a metal powder, a rigid outer mold and a head. The metal powder for preparing the protective layer of the ceramic membrane is placed in a mold consisting of a ceramic membrane, a high-temperature resistant rigid outer mold and a head, and sintered at high temperature under vacuum or a reducing atmosphere, and the outer mold is removed to form a ceramic composite membrane material with a metal protective layer. This method faces the following problems: (1) The metal powder is loosely packed in the mold and sintered. During the sintering process, the metal powder shrinks, causing cracks in the metal powder layer. Especially when the powder layer is uneven or there is a slight temperature difference, axial cracks are easily generated. Not only can it not effectively protect the ceramic membrane, but the uneven cracks also generate internal stress, causing the membrane tube to break. (2) Ceramic membrane layers with ultrafiltration pore sizes are usually sintered at conditions below 1000°C. Secondary high-temperature heat treatment will severely damage the ceramic membrane layer structure, seriously affecting the performance of the composite membrane material.

[0005] In addition, the porous metal layer of the metal-ceramic composite membrane requires not only high strength and good uniformity, but also high porosity and good permeability to ensure that no excessive resistance is generated to the infiltrating material. Patent CN110899703A discloses a method for preparing a high-porosity metal membrane, in which metal powder is filled in the metal, and after sintering, the metal mold is corroded by an acid solution to obtain a metal membrane. In order to improve the strength of the mold, the wall thickness of the metal outer mold is relatively large, and due to the airtightness of its structure, corrosion will start from the outer layer of the outer mold and the inner side of the inner membrane. If a complete metal membrane is to be obtained, the mold must be completely corroded, which will inevitably require a large amount of acid for corrosion, which will seriously affect the environment; in addition, the acid solution will more or less corrode the porous metal layer, which will also affect the strength and uniformity of the porous metal layer. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a composite membrane material that combines the high filtration accuracy of a ceramic membrane, the high strength of a metal membrane, and the weldability, especially a method for preparing a metal-based porous ceramic composite membrane with high porosity and good separation efficiency.

[0007] The object of the present invention is to provide a method for preparing a metal-based porous ceramic composite membrane, comprising the following steps:

[0008] S1, obtaining a suspension containing ceramic powder; coating the suspension on the inner surface of a porous ceramic tube to form a ceramic inner coating, thereby obtaining a porous ceramic tube having a ceramic inner coating;

[0009] S2, preparing a hollow cylindrical mold, rolling a metal plate into a tube, inserting the metal plate into the cylindrical mold and clinging to the inner surface of the hollow cylindrical mold;

[0010] S3, passing the porous ceramic tube with ceramic inner coating through the hollow part of the cylindrical mold formed in step S2, and setting an annular connector at one end of the cylindrical mold, so that a cavity is formed between the outer wall of the porous ceramic tube, the inner wall of the cylindrical mold and the annular connector;

[0011] S4, filling the cavity formed in step S3 with metal powder, and setting another annular connector at the other end of the cylindrical mold for sealing, thereby forming an assembly;

[0012] S5. The assembly is first sintered in an induction sintering furnace with a protective atmosphere, and then placed in a sintering furnace with a protective atmosphere for heat treatment. The ceramic inner coating forms a ceramic film layer, and the metal powder forms the metal film layer. The cylindrical mold is removed, and the metal plate is peeled off to obtain a metal-based porous ceramic composite membrane.

[0013] Specifically, the material of the metal powder is stainless steel or titanium, and the average particle size of the metal powder is 20 to 200 μm.

[0014] Specifically, the thickness of the metal film layer is 0.2-5 mm.

[0015] Specifically, the porous ceramic tube is single-channel or multi-channel, and the outer diameter of the porous ceramic tube is 4 to 50 mm, and the pore diameter is 0.05 to 5 μm.

[0016] Specifically, the pore size of the ceramic membrane layer ranges from 0.01 to 0.5 μm, and the thickness ranges from 2 to 200 μm.

[0017] Specifically, the annular connecting piece is made of ceramic or metal.

[0018] Specifically, the material of the cylindrical mold is one selected from quartz, cordierite and corundum.

[0019] Specifically, the metal plate is pure iron, alloy steel, titanium or titanium alloy, and the thickness of the metal plate is 0.05-0.5 mm.

[0020] Specifically, the sintering temperature of the induction sintering furnace is 900-1500° C., the heat treatment temperature is 400-900° C., and the insulation time is 1-5 hours.

[0021] The present invention overcomes the shortcomings of the prior art that the metal film layer is easy to crack due to sintering shrinkage and is difficult to demould, and proposes a new preparation process with the following advantages:

[0022] (1) The outer mold is made of rolled metal plates, which reduces the use cost of the mold. At high temperatures, the metal plates and metal powders diffuse with each other, and the metal plates can play a good positioning role for the metal powders, effectively reducing the axial shrinkage of the metal film layer after high-temperature sintering, avoiding cracking, and increasing the porosity of the metal film layer. At the same time, the metal plates can be easily peeled off from the metal film layer, which improves the demoulding efficiency. Even if a small amount remains on the surface, it does not affect the use.

[0023] (2) A porous ceramic tube with a ceramic coating formed on the inner wall of the hole is used as an inner mold to co-sinter the ceramic film layer and the metal film layer in one step, which effectively reduces the number of firings and reduces the production cost;

[0024] (3) The induction sintering technology is used to quickly sinter the metal film layer, which can ensure that the metal powder and the metal plate are sintered first to fix the powder layer and ensure that no cracks are generated; at the same time, the low heat transfer efficiency of ceramic materials is used to effectively slow down heat transfer, so that the ceramic film layer can be sintered at a lower temperature, and the low-temperature heat treatment technology can solve the internal stress of the metal layer while ensuring the sintering of the ceramic film layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Attached Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention;

[0026] Attached Figure 2 is a cross-sectional schematic diagram of embodiment 1 of the present invention;

[0027] Attached Figure 3 This is a structural photo of Example 1 of the present invention;

[0028] Attached Figure 4 This is a cross-sectional view of Example 1 of the present invention;

[0029] Attached Figure 5 This is a structural photo of Comparative Example 1 of the present invention;

[0030] Among them, 1-cylindrical mold; 2-metal plate; 3-metal film layer; 4-annular connector; 5-porous ceramic tube; 6-ceramic film layer. DETAILED DESCRIPTION

[0031] In order to solve the following problems in the prior art: organic membranes are not resistant to organic solvents, strong acid and alkali corrosion, low strength, and short life during use; compared with organic membranes, ceramic membranes, as a commonly used membrane material, have the advantages of good chemical stability, high mechanical strength, high temperature resistance, and high separation efficiency. Although ceramic membranes have higher strength than organic membranes, the brittleness of general ceramic substrates is relatively large, which makes ceramic membranes prone to sudden damage during use; in addition, metal membranes have the advantages of strong acid and alkali corrosion resistance, high strength, and long service life, but low filtration accuracy. Therefore, it is urgent to develop a preparation method for a metal-ceramic composite membrane with high porosity and high separation efficiency.

[0032] The present invention provides a method for preparing a metal-based porous ceramic composite membrane, comprising the following steps:

[0033] S1. Obtain a suspension containing ceramic powder (generally composed of ceramic powder, binder, dispersant, and solvent in proportion; the suspension containing ceramic powder can be formulated using the prior art); apply the suspension on the inner surface of a porous ceramic tube (outer diameter 4 to 50 mm, pore size 0.05 to 5 μm) to form a ceramic coating, thereby obtaining a porous ceramic tube having a ceramic coating;

[0034] S2. Prepare a hollow cylindrical mold (the material is one selected from quartz, cordierite and corundum), roll a metal plate (the material is pure iron, alloy steel, titanium or titanium alloy, with a thickness of 0.05-0.5 mm) into a tube, insert it into the cylindrical mold and cling it to the inner surface of the cylindrical mold;

[0035] S3, passing the porous ceramic tube with ceramic inner coating through the hollow part of the cylindrical mold formed in step S2, and setting an annular connector (made of ceramic or metal) at one end of the cylindrical mold, so that a cavity is formed between the outer wall of the porous ceramic tube, the inner wall of the cylindrical mold and the annular connector;

[0036] S4, filling the cavity formed in step S3 with metal powder (made of stainless steel or titanium, with an average particle size of 20 to 200 μm), and setting another annular connector (made of ceramic or metal) at the other end of the cylindrical mold for sealing, thereby forming an assembly;

[0037] S5. The assembly is first sintered in an induction sintering furnace with a protective atmosphere, and then placed in a sintering furnace with a protective atmosphere for heat treatment. The ceramic inner coating forms a ceramic film layer, and the metal powder forms a metal film layer. The cylindrical mold is removed and the metal plate is peeled off to obtain a metal-based porous ceramic composite membrane.

[0038] S5. The assembly is first sintered in an induction sintering furnace with a protective atmosphere (the sintering temperature of the induction sintering furnace is 900-1500°C), and then placed in a sintering furnace with a protective atmosphere for heat treatment (the heat treatment temperature is 400-900°C, and the insulation time is 1-5h). The ceramic coating forms a ceramic film layer (the pore size range is 0.01-0.5μm, and the thickness is 2-200μm), and the metal powder forms the metal film layer (the thickness is 0.2-5mm). The cylindrical mold is removed and the metal plate is peeled off to obtain a metal-based porous ceramic composite membrane (the pore size range is 0.01-0.5μm).

[0039] The porous ceramic tube in the present invention is single-channel or multi-channel. Preferably, a multi-channel ceramic tube is selected. Multi-channel means that there are multiple flow channels in the ceramic matrix, similar to Fengwo coal. Multi-channel can increase the flow area, thereby improving the filtering accuracy.

[0040] The porous ceramic tube in the present invention is a single-layer or multi-layer structure. The pore size of the ceramic tube with a single-layer structure is relatively large, about 0.5 to 5 μm; the pore size of the multi-layer structure is relatively small, ranging from 0.05 to 0.5 μm, depending on the number of layers. Preferably, the ceramic tube generally has a multi-layer structure, and the filtration accuracy is improved by gradually reducing the pore size.

[0041] The material of the annular connector in the present invention is ceramic or metal. When the annular connector is ceramic, high temperature resistant ceramic needs to be selected to ensure uniform thickness with the metal powder layer; when the annular connector is metal, a metal annular connector that is the same or similar to the metal material of the metal powder needs to be selected, which can be sintered with the metal powder to form a whole, so as to facilitate welding and connection with other metal parts later.

[0042] The sintering process of forming the metal film layer of the present invention is that the metal powders are slightly fused, the pores are retained, and they will not be completely melted into one. The metal film layer and the metal plate are the same, the two will adhere, but the bonding strength is not very high. After the high-temperature sintering is completed, the metal film layer and the metal plate can be completely peeled off by applying a certain mechanical force.

[0043] The high temperature sintering temperature in the present invention is related to the particle size of the metal powder. Generally, the sintering temperature of metal powder with larger particle size is higher than that of metal powder with smaller particle size, and the heat preservation time is longer. If the metal powder with small particle size is sintered at a very high temperature, it will be too dense, thereby affecting the filtering effect.

[0044] The present invention is further described in detail below in conjunction with specific examples, but the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry.

[0045] Example 1

[0046] This embodiment provides a method for preparing a metal-based porous ceramic composite membrane, comprising the following steps:

[0047] S1, obtaining a suspension containing ceramic powder; coating the suspension on the inner surface of a porous ceramic tube 5 (19 channels, outer diameter 30 mm, pore size 1 μm, length 1 m) to obtain a porous ceramic tube 5 with a ceramic coating;

[0048] S2, prepare a hollow cylindrical mold 1 (quartz tube, ), roll the metal plate 2 (stainless steel, thickness 0.3 mm, length 1 m, width 125 mm) into a tube, insert it into the cylindrical mold 1 and cling to the inner surface of the cylindrical mold 1;

[0049] S3, passing the porous ceramic tube 5 with the ceramic film layer 6 through the hollow part of the cylindrical mold 1 formed in step S2, and setting an annular connector 4 at one end of the cylindrical mold 1, so that a cavity is formed between the outer wall of the porous ceramic tube 5, the inner wall of the cylindrical mold 1 and the annular connector 4;

[0050] S4, filling the cavity formed in step S3 with metal powder (stainless steel powder, average particle size 100 μm), and setting another annular connector 4 at the other end of the cylindrical mold 1 for sealing, thereby forming an assembly;

[0051] S5. The assembly is first sintered in an induction sintering furnace with argon atmosphere protection (the sintering temperature of the induction sintering furnace is 1400°C), and then sintered and heat treated in a sintering furnace with a vacuum atmosphere (the heat treatment temperature is 800°C, the insulation time is 2h, and the heating rate is 3°C / min). The ceramic coating forms a ceramic film layer 6, and the metal powder forms a metal film layer 3 (with a thickness of 4.7mm). The cylindrical mold 1 is removed, and the metal plate 2 is peeled off to obtain a metal-based porous ceramic composite membrane (the membrane layer pore size is 0.21μm, and the membrane layer thickness is 100μm).

[0052] Example 2

[0053] The present embodiment provides a method for preparing a metal-based porous ceramic composite membrane, which is basically the same as Example 1, except that: in step S1, the pore size of the porous ceramic tube 5 is 0.2 μm; in step S4, the metal powder is stainless steel powder with an average particle size of 50 μm. At this time, in step S5, the induction sintering temperature is 1200°C, the heat treatment temperature is 700°C, the insulation time is 1h, and the heating rate is 2°C / min.

[0054] Example 3

[0055] The present embodiment provides a method for preparing a metal-based porous ceramic composite membrane, which is basically the same as Example 1, except that: in step S1, the pore size of the porous ceramic tube 5 is 0.05 μm; in step S4, the metal powder is stainless steel powder with an average particle size of 20 μm; at this time, in step S5, the induction sintering temperature is 900°C, the heat treatment temperature is 400°C, the insulation time is 2h, and the heating rate is 0.5°C / min.

[0056] Example 4

[0057] The present embodiment provides a method for preparing a metal-based porous ceramic composite membrane, which is basically the same as Example 1, except that: in step S1, the pore size of the porous ceramic tube 5 is 0.1 μm; in step S4, the average particle size of the metal powder is 60 μm; at this time, in step S5, the induction sintering temperature is 1250°C, the heat treatment temperature is 500°C, the insulation time is 4h, and the heating rate is 0.5°C / min.

[0058] Example 5

[0059] The present embodiment provides a method for preparing a metal-based porous ceramic composite membrane, which is basically the same as Example 1, except that: in step S1, the pore size of the porous ceramic tube 5 is 5 μm; in step S4, the average particle size of the metal powder is 200 μm; at this time, in step S5, the induction sintering temperature is 1500°C, the heat treatment temperature is 900°C, the insulation time is 5h, and the heating rate is 5°C / min.

[0060] Comparative Example 1

[0061] This comparative example provides a method for preparing a metal-based porous ceramic composite membrane, which is basically the same as Example 1, except that: in S2, there is no step of adding a metal plate 2, and the composite membrane is obtained as shown in the attached Figure 5 shown.

[0062] Comparative Example 2

[0063] This comparative example provides a method for preparing a metal-based porous ceramic composite membrane, which is basically the same as Example 3, except that: in S5, the induction sintering technology is not used, and a conventional sintering process is directly used to sinter in a protective atmosphere to obtain a composite membrane.

[0064] Comparative Example 3

[0065] This comparative example provides a method for preparing a metal-based porous ceramic composite membrane, which is basically the same as Example 1, except that in step S4, the average particle size of the metal powder is 200 μm.

[0066] The samples of Examples 1-5 and Comparative Examples 1-3 were tested for pore size using a bubble point method pore size analyzer and for porosity using an Archimedes principle method. The data obtained are shown in Table 1:

[0067] Table 1

[0068]

[0069]

[0070] It can be seen from the results of the above-mentioned embodiments and comparative test that adding the metal plate 2 can effectively prevent the metal film layer 3 from cracking, maintain the integrity of the metal film layer 3, and maintain the porosity of the metal film layer of the metal-based porous ceramic composite membrane at a high level; the use of an induction furnace for rapid sintering ensures that the metal film layer is sintered while not affecting the pore structure of the high-precision ceramic film layer, thereby ensuring the integrity of the ceramic film layer.

[0071] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a metal-based porous ceramic composite membrane, characterized in that: The steps include: S1, obtaining a suspension containing ceramic powder; coating the suspension on the inner surface of a porous ceramic tube to form a ceramic inner coating, thereby obtaining a porous ceramic tube having a ceramic inner coating; S2, prepare a hollow cylindrical mold, roll a metal plate into a tube, insert it into the cylindrical mold and cling it to the inner surface of the hollow cylindrical mold; the metal plate is pure iron, alloy steel, titanium or titanium alloy, and the thickness of the metal plate is 0.05-0.5 mm; S3, passing the porous ceramic tube with ceramic inner coating through the hollow part of the cylindrical mold formed in step S2, and setting an annular connector at one end of the cylindrical mold, so that a cavity is formed between the outer wall of the porous ceramic tube, the inner wall of the cylindrical mold and the annular connector; S4, filling the cavity formed in step S3 with metal powder, and setting another annular connector at the other end of the cylindrical mold for sealing, thereby forming an assembly; S5. The assembly is first sintered in an induction sintering furnace with a protective atmosphere, and then placed in a sintering furnace with a protective atmosphere for heat treatment, the ceramic inner coating forms a ceramic film layer, the metal powder forms a metal film layer, the cylindrical mold is removed, and the metal plate is peeled off to obtain a metal-based porous ceramic composite membrane; the sintering temperature of the induction sintering furnace is 900~1500℃, the heat treatment is 400~900℃, and the insulation time is 1~5h.

2. The preparation method according to claim 1, characterized in that: The material of the metal powder is stainless steel or titanium, and the average particle size of the metal powder is 20-200 μm.

3. The preparation method according to claim 1, characterized in that: The thickness of the metal film layer is 0.2-5 mm.

4. The preparation method according to claim 1, characterized in that: The porous ceramic tube is single-channel or multi-channel, and has an outer diameter of 4-50 mm and a pore diameter of 0.05-5 μm.

5. The preparation method according to claim 1, characterized in that: The pore size of the ceramic membrane layer ranges from 0.01 to 0.5 μm and the thickness ranges from 2 to 200 μm.

6. The preparation method according to claim 1, characterized in that: The material of the annular connecting piece is ceramic or metal.

7. The preparation method according to claim 1, characterized in that: The material of the cylindrical mold is one selected from quartz, cordierite and corundum.

8. The preparation method according to claim 1, characterized in that: The pore size of the metal-based porous ceramic composite membrane ranges from 0.01 to 0.5 μm.

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